1. Field of the Invention
The invention relates generally to wireless communications systems and more particularly to channel-switching in wireless communications systems.
2. Description of the Related Art
A typical wireless communications system consists of a source device and at least one sink device. In such a system, the source device typically transmits data to the sink devices via modulated radio frequency (“RF”) signals in a predetermined number of frequency channels. During data transmission, any particular frequency channel may be unreliable for any number of reasons: e.g., the source and sinks may move; the environment of the system may fluctuate causing time-varying fading; and other nearby sources of RF energy (e.g. other wireless devices) may cause interference. Interference by other wireless data systems is particularly problematic in the ISM (industrial, scientific and medical) frequency bands given the ever-increasing number of devices sharing these bands. Consequently, the quality of any particular wireless channel in these bands is somewhat unpredictable.
In coping with the above-described problems, known wireless communications systems typically employ conventional frequency hopping or channel-switching methods wherein the system hops to a new channel at predefined time intervals and follows a predefined channel hopping pattern. In such methods, the system hops to a new channel even when the present channel is of good quality. Such continuous hopping causes an unnecessary decrease in data transmission rates and impacts system stability. Furthermore, by following a predefined channel hopping pattern without regard to the quality of any particular channel, the system may return repeatedly to a channel of poor quality further degrading data transmission rates.
Another challenge to any wireless data transmission system and channel-switching method is the fact that, once the quality of the current channel degrades so as to interrupt communication between the source and sinks, reliable communication cannot be guaranteed. Any channel-switching method must therefore provide for the coordinated and reliable resolution of the source and sinks to an un-congested channel as quickly as possible without thereby requiring reliable communication between the source and sinks. In this way, data transmission can continue with minimal interruption.
There is accordingly a need for a wireless data transmission system and channel-switching method wherein the system switches to a new channel only when the quality of the current channel becomes unacceptable and which provides for the switching of the source and all sinks to a common channel of acceptable quality in an efficient, synchronized and reliable manner.